Coercive field (Ec) engineering based upon the monovalent Rb+ ion (Rb/K/Ba-exchange) and the divalent Ba2+ ion (Ba/K-exchange) has enabled the reliable periodic poling of RbKTiOPO4 (RKTP) for quasi-phase-matching (QPM). Previously, there have been no systematic studies to understand and compare the changes in polarization-switching properties induced by these two families of exchanges. In this paper, we compare different compositions of Rb/K/Ba- and Ba/K-exchanges in terms of how they affect the polarization-switching time, ts, and ionic conductivity in RKTP. We discuss the change in switching time, ts, that is ascribed to the interplay between the monovalent and divalent cations in the exchange. Moreover, we propose exchange-induced strain as the cause of bulk phase-matching shift and show that exchanges containing lower amounts of Rb induce less strain. This is corroborated by strain-deformation measurements on the exchanged samples. Finally, we demonstrate highly efficient periodically poled RKTP crystals free of bulk changes, using two different high ts - low strain exchanges.

This study compares image quality on the peripheral retina for far and near vision in schoolchildren. Biometric data and simultaneous foveal and peripheral (±25^◦ horizontal field) wavefront data for two levels of accommodation (0.22 D and 5 D) were collected from 31 children aged 6 to 11 years. Relative peripheral refraction (RPR) was found to be larger and more negative in the nasal visual field than in the temporal. This difference increased with accommodation. Furthermore, correlations between image quality and biometric parameters were investigated. The results highlight the importance of peripheral image quality during near work for myopia research. The data presented also form the baseline measurements of the Stockholm Myopia Study, which is a longitudinal pilot study on ocular growth and peripheral image quality in schoolchildren in Stockholm, Sweden.

A novel double-pass instrument and its data analysis method for the measurement of central and peripheral refraction is presented and validated in a group of healthy subjects. The instrument acquires in-vivo, non-cycloplegic, double-pass, through-focus images of the eye’s central and peripheral point-spread function (PSF) using an infrared laser source, a tunable lens and a CMOS camera. The through-focus images were analyzed to determine defocus and astigmatism at 0° and 30° visual field. These values were compared to those obtained with a lab-based Hartmann-Shack wavefront sensor. The two instruments provided data showing good correlation at both eccentricities, particularly in the estimation of defocus.

This study compares the effects on peripheral vision and image quality of four myopia control interventions: a) Perifocal spectacles/ArtOptica, b) Stellest spectacles/Essilor), c) MiyoSmart spectacles/Hoya and d) MiSight contact lenses/CooperVision. Five subjects participated with habitual or no correction as reference. Three techniques were used: 1) Hartmann-Shack sensors for wavefront errors, 2) double-pass imaging system for point-spread-functions (PSF), and 3) peripheral acuity evaluation. The results show that multiple evaluation methods are needed to fully quantify the optical effects of these myopia control interventions. Perifocal was found to make the relative peripheral refraction (RPR) more myopic in all subjects and to interact with the natural optical errors of the eye, hence showing larger variations in the effect on peripheral vision. MiSight had a smaller effect on RPR, but large effect on peripheral vision. Stellest and MiyoSmart also showed small effects on RPR but had broader double-pass PSFs for all participants, indicating reduced retinal contrast. Reduction in peripheral retinal contrast might thereby play a role in slowing myopia progression even when the peripheral refraction does not turn more myopic.